1. Field of the Invention
The present invention relates to an engine with a variable flow rate oil pump that is suitable for small vehicles, such as motorcycles.
2. Description of Related Art
In the related art, an engine is known that includes a variable flow rate oil pump having a main pump section and a subsidiary pump section with mutually different discharge rates, and an oil pressure-adjusting valve that adjusts supply oil pressure from the main pump section and the subsidiary pump section to oil pressure supply destinations (for example, refer to Japanese Utility Model (Registered) Publication No. 2598994).
During low-speed rotation of an engine, the discharge rate of the main pump section is supplied to the oil pressure supply destinations via a main discharge passage, and the discharge rate of the subsidiary pump section joins the oil pressure of the main discharge passage via a subsidiary discharge passage having the oil pressure-adjusting valve and is supplied to the oil pressure supply destinations.
The oil pressure-adjusting valve operates with a rise in the oil pressure of the main discharge passage (main pump section), and during high-speed rotation of the engine (during a rise in the oil pressure of the main discharge passage), the oil pressure of the subsidiary discharge passage (subsidiary pump section) is guided to a relief passage from the oil pressure-adjusting valve and is returned to a pump suction side, a portion of the oil pressure of the main discharge passage flows back in a region on the downstream side of the oil pressure-adjusting valve in the subsidiary discharge passage from a joining portion of the subsidiary discharge passage, is guided from the oil pressure-adjusting valve to the relief passage, and is returned to the pump suction side.